Area Forecast Discussion
Issued by NWS Boston, MA

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000 FXUS61 KBOX 011921 AFDBOX AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE TAUNTON MA 321 PM EDT TUE SEP 1 2015 .SYNOPSIS... HOT AND HUMID WEATHER PREVAILS BENEATH HIGH PRESSURE TONIGHT AND WEDNESDAY. A WEAK COLD FRONT WILL SWEEP ACROSS NEW ENGLAND ON THURSDAY. HIGH PRESSURE FROM CANADA MOVES OVER NEW ENGLAND FOR THE LABOR DAY WEEKEND. ANOTHER COLD FRONT APPROACHES NEW ENGLAND NEXT TUESDAY NIGHT. && .NEAR TERM /UNTIL 6 AM WEDNESDAY MORNING/... MID-LEVEL RIDGING PREVALENT BENEATH WHICH WINDS WILL BE LIGHT OVER- NIGHT. STOUT DRY-SUBSIDENCE INVERSION IN PLACE YIELDS THE POTENTIAL FOR SURFACE MOISTURE-POOLING. LOOKING AT A LOW-CLOUD / FOG POTENTIAL AS THE COMBINATION OF LIGHT WINDS AND MOSTLY CLEAR CONDITIONS NET AN ENVIRONMENT FAVORABLE FOR RADIATIONAL COOLING. GOT A FEW DEGREES COOLER INTO TUESDAY MORNING THAN INITIALLY THOUGHT...SO WILL GO A DEGREE OR TWO COOLER THAN MOS WITH LOWS AROUND THE LOW-60S AND A HIGHER FOG POTENTIAL ACROSS THE INTERIOR. && .SHORT TERM /6 AM WEDNESDAY MORNING THROUGH WEDNESDAY NIGHT/... WEDNESDAY... CERTAINLY HOT AND HUMID WITH SEVERAL LOCALES SEEING TEMPERATURES INTO THE LOW-90S BENEATH INFLUENTIAL MID-LEVEL RIDGING AND DRY-AIR SUBSIDENCE AND A H85 AIRMASS ALOFT OF +18-20C. A MOSTLY CLEAR DAY WITH SOME SCATTERED CUMULUS OUT TO THE W PARENT WITH INCREASING LOW- TO MID-LEVEL THETAE. ECHOING THE PREVIOUS FORECASTER...MOISTURE AND INSTABILITY APPEAR INTERESTING BENEATH FAVORABLE LAPSE RATES MORE TO THE N. BUT ABSENT ARE THE FORCING MECHANISMS. BUFKIT PROFILES SHOW A STRONG WARM-DRY CAP AROUND H85 WITH PARENT DEEP-LAYER SUBSIDENCE. SO LOOKING TO REMAIN DRY. LIGHT WINDS OVERALL WITH SEA-BREEZES ALONG THE SHORES. WEDNESDAY NIGHT... NOTEWORTHY MID-ATLANTIC LOW PUSHING E AND OFFSHORE TO OUR S AS A COLD FRONT APPROACHES FROM THE N. LOOK TO BE IN THE SQUEEZE-PLAY OF THE TWO WITH MORE DOMINANT SUBSIDENCE AND DRY AIR ASSOCIATED WITH RIDGING OF LINGERING HIGH PRESSURE. WILL KEEP WITH A DRY FORECAST WITH LIGHT WINDS. ANOTHER NIGHT OF LOW CLOUDS / PATCHY DENSE FOG IS POSSIBLE AS MOISTURE POOLS AGAIN BENEATH A DECOUPLING BOUNDARY-LAYER AND DRY-SUBSIDENCE INVERSION. OTHERWISE INCREASING MID-HIGH LEVEL CLOUDS WORKING IN TOWARDS MORNING. && .LONG TERM /THURSDAY THROUGH TUESDAY/... BIG PICTURE... LONG WAVE PATTERN SHOWS AN UPPER RIDGE OVER THE EASTERN USA WITH TROUGHS OVER THE MARITIMES AND PACIFIC COAST. THESE FEATURES SLOWLY MIGRATE WEST OVER THE FORECAST PERIOD. AT SHORTER SCALES...UPPER SHORTWAVE SWEEPS THROUGH NEW ENGLAND THURSDAY. HIGH PRESSURE REBUILDS OVER THE HOLIDAY WEEKEND BUT WITH A PREVAILING NORTH-NORTHWEST FLOW. THE FLOW TURNS MORE WEST-SOUTHWEST SUNDAY- MONDAY. THE UPPER RIDGE THEN ERODES AS A SHORTWAVE MOVES EAST ACROSS CANADA NEXT TUESDAY. THE GFS AND ECMWF ARE SIMILAR THROUGH NEXT TUESDAY. THE OVERNIGHT MODELS DIVERGED IN THEIR HANDLING OF THE SHORTWAVE NEXT WEEK...BUT THE 12Z RUNS HAVE NOW COME MORE INTO ACCORD. THE DAILIES... THURSDAY... SHORTWAVE MOVES OVER THE TOP OF THE EASTERN RIDGE AND CROSSES THE NORTHEAST USA. MOST OF THE JET DYNAMICS WITH THIS SYSTEM MOVES FROM QUEBEC ACROSS MAINE INTO THE MARITIMES...BUT THERE IS ENOUGH OOMPH WITH THIS SHORTWAVE TO PUSH A COLD FRONT THROUGH SOUTHERN NEW ENGLAND AND TURN OUR UPPER FLOW NORTHWEST. WIND FIELDS WILL BE LIGHT...BUT STABILITY WILL BE FAVORABLE WITH CAPES AROUND 1000 J/KG AND TOTALS AROUND 50. MOISTURE FIELDS WILL BE MODEST AND CONCENTRATED BELOW 750 MB. THIS SHOULD BE ENOUGH FOR SCATTERED SHOWERS/TSTMS. FRIDAY THROUGH MONDAY...CANADIAN HIGH PRESSURE IN CONTROL THROUGH THE PERIOD WITH SUBSIDENCE AND DRY AIR. A PREVAILING NORTHEAST FLOW FRIDAY AS THE HIGH APPROACHES...THIS MAY LIMIT MIXING A LITTLE ESPECIALLY IN EASTERN MASS. ON SATURDAY AND SUNDAY LIGHT WINDS UNDER THE HIGH MAY ALLOW AFTERNOON SEA BREEZES. MIXING PROFILES REACH 825 MB THURSDAY...900 MB FRIDAY AND SATURDAY...ROUGHLY 850 MB SUNDAY AND MONDAY. HERE ARE THE EQUIVALENT 850 MB TEMPS AND SFC TEMP FORECASTS... THURS 17C U80-L90/FRI 8-10C M70S-AROUND 80/SAT 11C AROUND 80-L80S/SUN 16-17C M80-U80/MON 17-18C U80-L90. TUESDAY...APPROACHING UPPER SHORTWAVE AND SURFACE COLD FRONT. MODEL TIMING FOR COLD FROPA IS EITHER NEXT TUESDAY NIGHT OR WEDNESDAY. TIMING UNCERTAINTY ABOUNDS THIS FAR OUT IN TIME. FOR NOW WITH A COLD FRONT APPROACHING WE WILL HAVE FAIR WARM WEATHER DURING THE DAY AND THEN INCLUDE A CHANCE OF SHOWERS NEXT TUESDAY NIGHT. WITH 850 MB TEMPS AROUND 18C EXPECT MAX DAYTIME TEMPS IN THE UPPER 80S AND LOWER 90S...COOLER NEAR THE SOUTH COAST. && .AVIATION /19Z TUESDAY THROUGH SUNDAY/... FORECASTER CONFIDENCE LEVELS... LOW...LESS THAN 30 PERCENT. MODERATE...30 TO 60 PERCENT. HIGH...GREATER THAN 60 PERCENT. SHORT TERM /THROUGH WEDNESDAY NIGHT/...HIGH CONFIDENCE. VFR. ONSHORE FLOW DIMINISHES OVERNIGHT. LIGHT WINDS AND SKC ALLOW FOR IFR FOG DEVELOPMENT IN SHELTERED / LOW-LYING TERMINALS ACROSS INTERIOR NEW ENGLAND. BURNING OFF DURING THE MORNING...LIGHT W/SW- FLOW RETURNS WITH SEA-BREEZES ALONG THE SHORES FOR WEDNESDAY. SCT 5 KFT CIGS TO THE W. A RETURN OF MVFR-IFR CIGS / VSBYS FOR THE WEDNESDAY OVERNIGHT PERIOD INTO THURSDAY MORNING. KBOS TERMINAL...HIGH CONFIDENCE IN TAF. SEA BREEZE POSSIBLE ALBEIT LATER FOR WEDNESDAY. KBDL TERMINAL...HIGH CONFIDENCE IN TAF. OUTLOOK...THURSDAY THROUGH SUNDAY...HIGH CONFIDENCE. THURSDAY...MAINLY VFR. BRIEF MVFR CIGS/VSBYS IN AFTERNOON/EVENING SHOWERS/TSTMS. PATCHY IFR IN EARLY MORNING FOG. FRIDAY THROUGH SUNDAY...VFR. PATCHY IFR IN EARLY MORNING FOG. && .MARINE... FORECASTER CONFIDENCE LEVELS... LOW...LESS THAN 30 PERCENT. MODERATE...30 TO 60 PERCENT. HIGH...GREATER THAN 60 PERCENT. SHORT TERM /THROUGH WEDNESDAY NIGHT/...HIGH CONFIDENCE. SEAS AT OR BELOW 4-FEET. ONLY ISSUES ARE W/SW-WINDS OVER THE WATERS WITH GUSTS UP TO AROUND 15 KTS ACROSS THE E-OUTER WATERS FOR A MAJORITY OF THE PERIOD...PERHAPS SOME PATCHY DENSE FOG ALONG THE SHORES WITH ONSHORE FLOW DURING THE DAY. MAINLY QUIET BOATING WEATHER PREVAILS THROUGH WED. OUTLOOK...THURSDAY THROUGH SUNDAY...MODERATE TO HIGH CONFIDENCE. COLD FRONT MOVES ACROSS THE WATERS LATE THURSDAY OR THURSDAY NIGHT. WINDS TURN NORTHEAST BEHIND THE FRONT AND CLIMB TO 20-25 KNOTS FOR FRIDAY. THE NORTHEAST WINDS MAY ALSO BRING A PERIOD OF 5 FOOT SEAS...BEST CHANCE ON THE WATERS EAST OF MASSACHUSETTS. A SMALL CRAFT ADVISORY MAY BE NEEDED FRIDAY. HIGH PRESSURE THEN MOVES OVERHEAD AND BRINGS LIGHT WIND AND SEAS OVER THE WEEKEND. && .BOX WATCHES/WARNINGS/ADVISORIES... CT...NONE. MA...NONE. RI...NONE. MARINE...NONE. && $$ SYNOPSIS...WTB/SIPPRELL NEAR TERM...SIPPRELL SHORT TERM...SIPPRELL LONG TERM...WTB AVIATION...WTB/SIPPRELL MARINE...WTB/SIPPRELL

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